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Lens Maker's Formula

What is the f...

Question

What is the focal length of double concave lens kept in air with two spherical surface of radii $R_{1} = 30 c m$ and $R_{2} = 60 c m$ . Take refractive index of lens as $μ = 1.5$ .

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Solution

Using lens makers formula

$\frac{1}{f} = (μ - 1) [\frac{1}{R_{1}} - \frac{1}{R_{2}}]$ where $R_{1} = - v e$

$\frac{1}{f} = (1.5 - 1) [\frac{1}{(- 30)} - \frac{1}{60}]$

$\frac{1}{f} = (0.5) [\frac{3}{60}] = - 0.5 \times \frac{1}{20}$

$f = - 40 c m$

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Similar questions

R_{1} = 30 c m

R_{2} = 60 c m ?

1.5

R_{1} = - 20 c m

R_{2} = 80 c m

30 c m

60 c m

1.5

30 c m

1.5

R_{1} = R_{2} = 2 c m

μ = 1.5

R_{1} = 20 c m, R_{2} = 10 c m

μ = 1.6

R_{1} = 20 c m, R_{2} = 30 c m

μ = 1.5

R_{1} = 20 c m, R_{2} = 40 c m

μ = 1.5

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